A solid-state imaging element has such a structure that a LSI chip as a light receiving element is accommodated in a package; on its light-receiving surface, a color separation mosaic filter is overlaid and wire-bonded; and a package opening is sealed with a cover glass by means of an adhesive. The cover glass to be used here is required to have an optically uniform material property with little internal defects and a high transmittance property, in order to not only protect the LSI chip by the air-tight sealing, but also efficiently introduce light to the light-receiving surface. Further, the glass to be used for such an application should be free from cracking or distortion when it is sealed on the package. That is, the thermal expansion coefficient should be matched between the glass and the package material. As the package material, a ceramic such as alumina having an average thermal expansion coefficient of from 60 to 75×10−7K−1 has been used, and as a cover glass to match with it, a borosilicate glass having an average thermal expansion coefficient of from 45 to 75×10−7K−1 is available. Further, a P2O5—Al2O3 base glass containing CuO as an essential component, has been proposed as a window glass for a semiconductor package (Patent Document 1).
In recent years, for the purpose of weight reduction or cost reduction in imaging devices such as digital cameras, a study has been made to use a resin as a package material. The average thermal expansion coefficients of resin materials are from 110 to 180×10−7K−1 i.e. higher than of ceramics. Further, a resin package having the thermal expansion coefficient lowered by e.g. incorporating a large amount of SiO2 powder to a resin, is also available, but even if such an additive is incorporated, the average thermal expansion coefficient of the resin package is at a level of at least 95×10−7K−1. Therefore, if the conventional borosilicate glass is applied to such a resin package, deformation of the package or peeling of the cover glass has been likely to occur, due to the large difference in the thermal expansion coefficient between the two.
Whereas, as a cover glass suitable for a resin package, a fluorophosphate glass has been proposed (Patent Document 2). This glass is a fluorophosphate glass having an average thermal expansion coefficient of from 120 to 180×10−7K−1 within a range of from 100 to 300° C. and thus is regarded as being excellent in the mounting property on a resin package.
Further, in a process for assembling an imaging device using a solid-state imaging element, after temporarily fixing a cover glass, the presence or absence of dust deposited on the surface of the light-receiving element is inspected on the basis of an output image information from the solid-state imaging element, and if the presence of dust is found, the temporarily fixed cover glass is dismounted from the package, and the solid-state imaging element is subjected to cleaning (Patent Document 3).